The present invention relates generally to an overheat protection circuit. The present invention also relates to an overheat protection circuit for preventing a semiconductor apparatus, that has a constant voltage regulator, from being destroyed by overheating caused by an over output current. Furthermore, the present invention relates to an electronic device having an overheat protection circuit, and an overheat protection method.
Recently, an overheat protection circuit has been known. The purpose of the overheat protection circuit is to protect a semiconductor apparatus based on a temperature value of a semiconductor chip measured by the circuit.
The known overheat protection circuit tends to increase a consumption current so that a constant voltage regulator always provides electricity for the overheat protection circuit during operation.
The overheat protection circuit works only in the case where an electric current output by a constant voltage circuit is high. Therefore, it is a waste to provide electricity for the overheat protection circuit in a case where the output current is low.
For example, in Japanese Laid-Open Patent Publication No. 2002-312044 (Patent Document 1), an overheat detecting circuit is provided a bias current only in the case where a detected output current is more than a predetermined output current.
FIG. 4 is a schematic illustration of an embodiment described in FIG. 1 of Patent Document 1. As shown in FIG. 4, a constant voltage circuit of a power supply circuit is configured to a reference voltage Vref, an error amplification circuit 1, an output control transistor Q11, a transistor Q13, a resistance R13 and output voltage detecting resistances R11, R12.
An output voltage Vo from the constant voltage circuit is divided by the resistances R11, R12.
The error amplification circuit 1 amplifies the difference between the divided voltage and the reference voltage Vref, and controls a base current of the transistor Q13 so that the difference becomes 0V.
Because the collector of transistor Q13 is connected to a base of the output control transistor Q11, the error amplification may control the output control transistor Q11 through the transistor Q13.
The transistor Q12 and the output control transistor Q11 make a multi-collector structure. As the collector current of the transistor Q12 is proportional to the collector current of the output control transistor Q11, the output current can be detected indirectly by detecting the collector current value of the transistor Q12.
The collector current of the transistor Q12 is supplied to the resistance R14. Thus, it causes a voltage drop in the resistance R14.
The ends of the resistance R14 are connected between the base and the emitter of the transistor Q14.
The collector of the transistor Q14 is connected to the bias circuit 2. The emitter of the transistor Q14 is connected to a ground electrical current potential.
When the voltage drop in the resistance R14 exceeds a base threshold voltage of the transistor Q14, the transistor Q14 turns on so that the collector current of the transistor Q12 is increased. Therefore, the bias circuit 2 is electrified and operated.
Since the output of the bias circuit 2 is applied to the overheat detecting circuit 3, the overheat detecting circuit 3 is started by the bias circuit 2.
The overheat detecting circuit 3 has two outputs.
One output of the overheat detecting circuit 3 is connected to the base of the transistor Q13. The second output of the overheat detecting circuit 3 is connected to a CPU that controls a whole circuit.
When the overheat detecting circuit 3 detects an overheat state of the semiconductor apparatus, the level of the first output of the overheat detecting circuit 3 becomes low. Accordingly, the base voltage of the transistor Q13 is reduced, and the transistor Q13 turns off.
Because of this, supply of a base electric current of the output control transistor Q11 stops, and the output control transistor Q11 turns off. Thus, the constant voltage circuit stops power supply to a load.
The second output of the overheat detecting circuit 3 is input into the CPU. The CPU performs a suitable processing, for example a load is reduced, according to an overheat signal.